Growth and uptake kinetics for nitrate, ammonium and phosphate by Gymnodinium catenatum isolated from Hiroshima Bay were experimentally investigated. Maximum uptake rate (ρ_max) and half saturation constant (Ks), which were obtained by short-term uptake experiments, were 6.48 pmol/cell per h and 7.60 μM for nitrate, 3.37 pmol/cell per h and 33.6 μM for ammonium, and 1.42 pmol/cell per h and 3.40 μM for phosphate, respectively. Specific maximum growth rate (μ'_m) and minimum cell quota (Q₀), which were obtained by semicontinuous growth experiments, were 0.36/day and 31.3 pmol/cell for the N-limited conditions, respectively. The μ'_m and Q_P0 for P-limited conditions were 0.37/day and 1.83 pmol/cell, respectively. These results indicate that G. catenatum is a poor competitor in terms of utilization of inorganic nutrients and is unlikely to form blooms in Hiroshima Bay where phosphate is chronically depleted unless the growth is supported by organic species (i.e. dissolved organic phosphorus) of the nutrients.

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